Shielding system



P 1937. J. R. TRAVES 2,075,965

SHIELDING SYSTEM Filed April 25, 1936 Pan-R LINE WSW/5L0 MR5 f 44 I g l l su/no MR: W i TELEPHONE u/v:

FIG. 2 FIG. 3

POWER u/vss POWER LINES \fti a 1\6 /a TELEPHONE n l I JLITELEPHONE .n. a.

L/NES a LINES Inna HULL I n n n a l u n n g A 3 /s/-//1.o MR5 ,sH/A'La I a 1 WIRE SHIELD 3 SHIELD WIRES WIRE EARTH EARTH WVENTOR J R. TRA VES O+m$M ATTORNEY distribution lines.

Accidental grounds, switching surges, short Patented Apr. 1937 PATENT orrlcs smnmmo srs'rlm John 8.. Trans, Toronto, Ontario, Canada, as-

signor to Western Electric Oompanyglneorporated, New York, 1s. m, a p a ion or'New.

York

mam. as, 1530, Serial 1am s (c1. ran-am) This inventionrelates to shielding systems and particularly to means for mitigating interference I to telephone and telegraph service caused by residual or fault currents in power transmission and circuits, etc., on power transmission and distribution lines may result in a flow of residual current which, under some circumstances, may induce dangerous potentials in adjacent telephone or telegraph circuits.

An object of this invention is to prevent the appearance of these potentials or to reduce them to safe values.

5 A feature of this invention resides in providing a grounded shield wire adjacent both power and telephone lines and inductively connecting the shield wires in such a manner that the voltage induced in the telephone lines by the current in the shield wire adjacent the telephone lines produced by its interconnection with the conductor adjacent the power line is 180 degreesout of phase with the voltage induced in the telephone lines by the-power line residual current through the direct coupling between the power and telephone lines.

The invention will be more fully understood from the following description having reference to the accompanying drawing in which:

Fig. 1 is a diagrammatic side elevation of a power line and a telephone line protected against induction'in accordance with my invention;

Fig. 2 is a' diagrammatic and elevation of a power line and pole with a shield wire mounted on the power pole and a telephone pole with telephone lines and a shield wire mounted thereon;

Fig. 3 is a diagrammatic end elevation of a power line with a shield wire mounted on the power pole and a telephone pole with two shield wires mounted on the telephone pole; and

Fig. 4 is a diagrammatic'view of a modification of my invention in which the power line crosses the telephone line.

Referring now to Fig. 1 of the drawing there is shown a high conductivity conductor or shield will not represent a safety or service hazard. If necessary, two ormore conductors located at diflerent points on the pole line, as shown in Fig. 3, and connected in parallel maybe used in order to obtain an even distribution of potential 5 over the various telephone conductors. The shield wire 3 is connected to low resistance grounds at the ends, and has one winding of a transformer 4 connected in series therewith. I The remaining windings 22 and 44 of the trans- 1o formers 2 and 4, respectively, are interconnected in such a manner that the voltage induced in the telephone lines by the current in conductor 3. produced by its interconnection with conductor I is 180 degrees out of phase with the voltage in- 15 duced in the telephone lines by the power line residual current through the direct coupling between the powerand telephone lines. If it is found necessary to locate transformers 2 and 4 at some distance from each other, it will benecessary to construct a tie line between them.

The length, cross-section and material of conductors I and 3 and the ratio of transformers 2 and 4 is determined by the resistance of the grounds, the resistivity of the soil, the relative 25 location of the power and telephone lines, the maximum amount of residual current which may flow in the exposure, the desired amount of shielding and the relative costs of the various possible arrangements. If the various grounds 30 mentioned are in close proximity, ground potential effects should be taken into consideration. Furthermore, the mutual coupling between the various conductors involved must be considered since conductors I and 3 introduce considerable shielding disregarding the coupling introduced by the transformers.

Fig. 4 shows an embodiment of the invention in a case where a power line I6 crosses a telephone line I8. In this arrangement one shield 40 wire II is run along the power line I6 and has a winding of a transformer serially connected therein. Another shield wire 23 is run along the telephone line I8 and it has another winding of the transformer connected therein, the windings 45 of the transformers being connected so as to balance out the disturbing inductive effects. of the power line.

What is claimed is: I

1. In combination, a power line, a. telephone line subject to induction therefrom, and shield wires adjacent both power and telephone lines, said shield wires being inductively connected.

2. In combination, a power line, a telephone line subjectto induction therefrom, a shield wire adjacent said power line, a shield wire adjacent said telephone line, and means including a transformer inductively connecting said shield wires.

3. In combination, a power line, a telephone 5 line subject to induction therefrom, a grounded shield wire adjacent said power line, and a grounded shield wire adjacent said telephone line, said shield wires being inductively connected.

4. In combination, a power line, a telephone 10 line subject to induction therefrom, a grounded shield wire adjacent each of said lines, and a transformer having a winding in series with each of said shield wires, said windings being connected in opposing relationship. 15 5. In combination, a power line subject to a residual current therein, a telephone line subject to induction therefrom, a grounded shield wire adjacent said power line, a grounded shield wire adjacent said telephone line, a pair of transformers each having one winding in series with one of said shield wires, the remaining windings or said transformers being interconnected so that the voltage induced in the telephone line by the current in the shield wire adjacent the telephone line produced by its interconnection with the shield wire adjacent the power line is 180 degrees out of phase with the voltage induced in the telephone line by the power line residual current through the direct coupling between the power and telephone lines.

JOHN R. TRAVES. 

